1. Information Storage and Spintronics 18
Atsufumi Hirohata
Department of Electronic Engineering
15:00 Tuesday, 03/December/2019 (P/L 006)

2. Quick Review over the Last Lecture
Family of Hall effects : *
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* C.-Z. Chang and M. Li, J. Phys.: Condens. Matter 28, (2016).

3. 18 Other Spintronic Devices
Spin caloritronics
Berry’s phase
Spin mechatronics
Zeeman splitting
Spin optics

4. Vertical devices Spins h Spin injection from a ferromagnet
Magnetic field
application
Spins
Electric field
application h
Thermal gradient
introduction
Electromagnetic
wave
introduction

5. Spin Seebeck Effect * K. Uchida et al., Nature 455, 778 (2008);
** K Uchida et al.,  J. Phys.: Condens. Matter 26,  (2014).

6. Spin Seebeck Effect
* K. Uchida et al., Nature Mater. 9, 894 (2010).

7. Vertical devices Spins h Spin injection from a ferromagnet
Magnetic field
application
Spins
Electric field
application
Berry phase h
Thermal gradient
introduction
Electromagnetic
wave
introduction

8. Theoretical Prediction on a Persistent Current
induced by a magnetic flux threading a mesoscopic ring
 Aharonov-Bohm effect *
The persistent current oscillates with the flux.
induced by a magnetic field rotating slowly in time **
 Berry (geometrical) phase
Non-uniform external magnetic fields are required.
Spin-polarised persistent current can be generated.
* Y. Aharonov and D. Bohm, Phys. Rev. 115, 485 (1959); A. Tonomura et al., Phys. Rev. Lett. 56, 792 (1986);
** D. Loss and P. M. Goldbart, Phys. Rev. B 45, (1992).

9. Vertical devices Spins h Spin injection from a ferromagnet Mechanical
rotation
Magnetic field
application
Spins
Electric field
application
Berry phase h
Thermal gradient
introduction
Electromagnetic
wave
introduction

10. Spin Current in a Rotating Body
The Einstein de Haas effect describes the rotation of a magnetised body due to the conservation of angular momentum, by the application of a magnetic field.*
The Barnett effect describes the inverse effect, where a body exhibits an increased magnetisation due to mechanical rotation.**
The coupling between rotation and magnetisation and magnetisation and spin currents is well established.
In 2011 Matsuo et al. proposed a new method for the direct generation of a spin current via mechanical rotation.***
JS = spin current density
e = electron charge
n = electron density
R = radius of rotation
ηSO = spin orbit coupling strength, 0.59
f = frequency
εF = Fermi energy
ωC = qB/m for electron wave packet
* A. Einstein and W. J. de Haas, KNAW Proc. 18, 696 (1915);
** S. J. Barnett, Phys. Rev. 6, 239 (1915);
*** M. Matsuo et al., Phys. Rev. Lett. 106, (2011).

11. Spin Mechatronics Measurement
In a similar vein, one can observe the Barnett field in a rotating body observing a shift in the NMR.
The nuclear g factor dependence of the NMR shift is observed to measure the Barnett field.*
The presence of a spin current may be detected by the magneto-optical Kerr effect (MOKE).
This allows for direct probing of the conduction electrons.
Schematic of the NMR measurement setup for the Barnett effect [6]
* H. Chudo et al., Appl. Phys. Exp. 7,  (2014).

12. Vertical devices Spins h Spin injection from a ferromagnet Mechanical
rotation
Magnetic field
application
Spins
Electric field
application
Berry phase h
Thermal gradient
introduction
Electromagnetic
wave
introduction
Zeeman splitting

13. Spin Transport - Spin-pol'd electrons / holes  SC  Circ
Spin Transport - Spin-pol'd electrons / holes  SC  Circ.-pol'd photons
Spin LED structures :
Structures
Spin polarisation
Refs.
Spin-polarised electron injection :
300 nm BeMgZnSe + BeMnZnSe / 100 nm n-AlGaAs / 15 nm i-GaAs QW / … / p-GaAs
~ <5 K
R. Fiederling et al., Nature 402, 787 (1999).
360 nm CdMnTe / 1400 nm CdTe
~ 5 K
M. Oestreich et al., Appl. Phys. Lett. 74, 1251 (1999).
n-ZnMnSe / AlGaAs / nm GaAs QW / AlGaAs
~ 4.5 K
B. T. Jonker et al., Phys. Rev. B 62, 8180 (2000); Appl. Phys. Lett. 81, 265 (2002).
20 nm Fe / GaAs / InGaAs QW / GaAs
~ 25 K
H. J. Zhu et al., Phys. Rev. Lett. 87, (2001).
12.5 nm Fe / AlGaAs / GaAs QW / GaAs
~ 4.5 K
~ 240 K
A. T. Hanbicki et al., Appl. Phys. Lett. 80, 1240 (2002).
8 nm NiFe + 2 nm CoFe / 1.4 nm AlOx / 15 nm AlGaAs / 100 nm GaAs QW / GaAs
80 K
V. F. Motsnyi et al., Appl. Phys. Lett. 81, 265 (2002).
20 nm (Co, Fe & NiFe) / 2 nm Al2O3 / 50 nm n-AlGaAs / 50 nm si-AlGaAs / 20 nm si-GaAs QW / … / GaAs
0.8%, 0.5% & RT
T. Manago et al., Appl. Phys. Lett. 81, 694 (2002).
Spin-polarised hole injection :
300 nm p-GaMnAs / nm GaAs / 10 nm InGaAs QW
~ <31 K
Y. Ohno et al., Nature 402, 790 (1999).

14. Optically-Induced Spin-Polarised Electrons
Photoexcitation :
Electrons spin-polarised by introducing circularly polarised light
Circularly polarised electroluminescence (EL) :
Circularly polarised light generated by spin-polarised electrons at a quantum well
(QW)

15. Photon Energy DependenceEg
Eg + 
NiFe / GaAs (100)
at room temperature 40 40
p = m -3
Asymmetry [%] 20 20
Polarisation [%]
1.5
2.0
2.5
n = m -3
Photon Energy [eV]
Spin polarisation  asymmetry in spin transport effect :
A = ( I n - I 0 ) / ( I n + I 0 )
A decreases with increasing photon energy.
 spin polarisation in GaAs
n = m -3
* D. T. Pierce et al., Phys. Lett. 51A, 465 (1975); A.Hirohata et al., Phys. Rev. B 63, (2001).

16. Spin Electronics with Optical Methods
Spin-polarised inverse photoemission
Spin-polarised STM
Photoexcitation
Spin-polarised LED
* A. Hirohata, "Optically induced and detected spin current,” in S. Maekawa et al. (Eds.) Spin Current (Oxford University Press, Oxford, 2012) pp

17. Quick Review over the Last Lecture
Vertical devices
Quick Review over the Last Lecture
Spin injection
from a ferromagnet
Mechanical
rotation
Magnetic field
application
Lateral Devices
Spins
Vertical Devices
Electric field
application
Berry phase h
Thermal gradient
introduction
Electromagnetic
wave
introduction
Zeeman splitting

18. Spin moment Stray field HDD read head Magnetic tagging
Spin-torque oscillator
Ferrofluid
Magnetic hyperthermia
MRAM
Magnetic sensor
Racetrack memory
TMR
GMR
Lateral spin-valve
HDD write head 1D 0D
Spin-orbit 1D
Spin Seebeck 2D 2D
Spin Hall 3D 3D
Recording media
Spin transistor
Electromagnetic shield
Permanent magnet
Electromagnetic generator
Electromagnetic motor
Spin moment
Stray field

19. Spintonics Studies in the World
Spintronics is one of the most exciting subject in nano-electronics :
Spin Dynamics
Spin Accumulation
Spin Transfer
Spin Operation
Spin Engineering
Theoretical Studies